
// symbol 
let x = symbol()
class A {
    constructor() {
        this[x] = {}
    }
    getx() {
        return this[x]
    }
}

// 闭包
(() => {
    let _x 
    class A {
        constructor(x) {
            _x = x
        }
        getx() {
            return _x
        }
    }

    return A

})()
